1. Field of the Invention
The present invention relates to self-loading firearms. More particularly, the present invention relates to the operating system of indirect gas-operated firearms in the AR15/M16 series of firearms and specifically the bolt carrier for use in such firearms.
2. Description of the Related Art
The AR15/M16 family of weapons and their derivatives including indirect gas operated versions, have been in use by the military and civilian population for many years. An essential part of this firearm's design is the bolt carrier which typically includes a bolt mounted in the carrier for axial sliding movement and rotation, a firing pin slidably mounted within the bolt and bolt carrier for restricted reciprocating axial movement, and a cam pin for producing relative rotation between the bolt and the bolt carrier.
The bolt carrier is generally cylindrical in shape with a longitudinally extending circular bore throughout its length. An elongated opening is provided in the top and bottom of the carrier to allow the hammer to extend into the interior of the bolt carrier and strike the firing pin. The rear of the carrier is received within the firearm receiver and the front of the carrier houses the bolt. The upper surface of the carrier immediately adjacent the front face includes a flat shelf for engagement with a charging handle.
The top of the carrier in front of the opening is machined to receive a carrier key which operates in conjunction with the operating rod of the firearm's gas operating system to cycle the bolt action in automatic and semi-automatic operation. A carrier with a separate carrier key that is attached to the carrier with fasteners is set forth in U.S. Pat. No. 7,461,581 (“the '581 patent”), which is owned by the assignee of the present application and is hereby expressly incorporated by reference as if fully set forth herein. This two-part construction necessitates careful machining of both the carrier and the carrier key to ensure a close fit within a narrow tolerance.
In a conventional indirect gas operated firearm, the operating rod of the gas operating system contacts the strike face of the carrier key after the weapon is fired and gas pressure displaces the operating rod rearwardly. Because the strike face is above the central axis of the bolt carrier, an undesirable phenomenon known as carrier tilt occurs during the normal operation of the firearm. Carrier tilt can be defined as the rear of the carrier tilting downwardly when the strike face has been contacted by the operating rod, resulting in the rearward movement of the carrier being resisted when the now off-axis carrier strikes the forward leading edge of the receiver extension. Eliminating carrier tilt would be a very desirable attribute.
About the exterior of the bolt carrier are a series of longitudinally extending lands or rails, usually four, which make contact with the cylindrical interior surface of the upper receiver of the firearm and serve to align the bolt carrier within the receiver. The rails include two upper rails and two lower rails spaced from one another about the exterior circumference of the bolt carrier. The upper rails extend from the elongated opening to the rear edge of the charging handle engagement shelf. The two lower rails are generally parallel with the upper rails and extend from the elongated opening all the way to the front face of the carrier.
Conventionally, the rails are contiguous and held to tight tolerance with the running surfaces in the upper receiver. Firearms such as the Stoner type rifle are very prone to stoppages and malfunctions when sand or dirt works into the receiver. Therefore, a need exists for a rail configuration that supports the carrier while reducing the likelihood of firearm malfunction when exposed to dirt and sand.
The rear end of the carrier typically does not contact the inside of the receiver but rather is supported by the longitudinal rails. To further support the carrier against carrier tilt, the rear of the carrier may be provided with a generally cylindrical boss having an outer diameter larger than the main body of the bolt carrier as described in a copending application filed on Oct. 10, 2008, entitled “Automatic Rifle Bolt Carrier with Fluted Boss”, by Jesus S. Gomez and Jason Miller (hereinafter, “the Gomez application”), which is also owned by the assignee of the present application and is hereby expressly incorporated by reference as if fully set forth herein. The boss in the Gomez application has an outer diameter large enough to make contact with the cylindrical inside of the receiver extension to ensure that the carrier centers therein.
Firearms based on the AR15/M16 family are the primary weapon of choice for military units in the United States and abroad. Highly trained units from all branches of service often find themselves operating in aquatic conditions prior to coming on land. The inability of the AR15/M16 series of weapons to be fired when water is present in the operating system puts these military personnel in a compromising position. With the current AR15/M16 series of weapons, and their derivatives, the firearm must be drained of all water prior to being discharged. This draining is not convenient or practical for a soldier who may come under fire immediately upon landing on a beach. Such situations are typically referred to as “over the beach operations”. Incorporating features into the operating system which allow the firearm to be immediately discharged upon exit from an aquatic environment would be highly desirable. One such feature is set forth in the Gomez application, namely, a series of longitudinal cuts or flutes spaced about the circumference of the boss to allow for water to pass by the boss. Additional water removal features would also be desirable.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.